Client noncompete - enforceable for a staffing agency W2 employee?

I'm an W2 employee of a staffing agency, currently doing work for one client. After my hire the client revised their confidentiality agreement to include a noncompete clause (no contract work allowed for direct competitors during my contract w/this client). I am not on retainer, so I feel this is not appropriate; should my hours drop w/this client to where I can't pay bills, I need to solicit additional work. Staffing agency told me I am W2 with them so I am not an independent contractor and should sign. I feel that's irrelevant; in the end, I'm the one whose income is threatened. I am not an employee of the company asking me to sign a noncompete. What do you think? Note that the agency, the company, and I are all based in different states and I telecommute.